Average Weather in St. Louis Missouri, United States
In St. Louis, the summers are hot and muggy, the winters are chilly, and it is partly cloudy year round. Over the course of the year, the temperature typically varies from 25°F to 89°F and is rarely below 9°F or above 97°F.
The hot season lasts for 3.7 months, from May 27 to September 19, with an average daily high temperature above 79°F. The hottest day of the year is July 20, with an average high of 89°F and low of 70°F.
The cold season lasts for 3.0 months, from November 28 to February 28, with an average daily high temperature below 51°F. The coldest day of the year is January 22, with an average low of 25°F and high of 41°F.
Average High and Low Temperature
The figure below shows you a compact characterization of the entire year of hourly average temperatures. The horizontal axis is the day of the year, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.
Average Hourly Temperature
In St. Louis, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year.
The clearer part of the year in St. Louis begins around June 13 and lasts for 4.6 months, ending around October 31. On August 27, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 71% of the time, and overcast or mostly cloudy 29% of the time.
The cloudier part of the year begins around October 31 and lasts for 7.4 months, ending around June 13. On February 12, the cloudiest day of the year, the sky is overcast or mostly cloudy 54% of the time, and clear, mostly clear, or partly cloudy 46% of the time.
Cloud Cover Categories
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in St. Louis varies throughout the year.
The wetter season lasts 5.3 months, from March 20 to August 29, with a greater than 28% chance of a given day being a wet day. The chance of a wet day peaks at 40% on May 21.
The drier season lasts 6.7 months, from August 29 to March 20. The smallest chance of a wet day is 16% on January 16.
Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 40% on May 21.
Daily Chance of Precipitation
To show variation within the months and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day of the year. St. Louis experiences significant seasonal variation in monthly rainfall.
Rain falls throughout the year in St. Louis. The most rain falls during the 31 days centered around May 13, with an average total accumulation of 4.1 inches.
The least rain falls around January 24, with an average total accumulation of 1.6 inches.
Average Monthly Rainfall
We report snowfall in liquid-equivalent terms. The actual depth of new snowfall is typically between 5 and 10 times the liquid-equivalent amount, assuming the ground is frozen. Colder, drier snow tends to be on the higher end of that range and warmer, wetter snow on the lower end.
As with rainfall, we consider the snowfall accumulated over a sliding 31-day period centered around each day of the year. St. Louis experiences some seasonal variation in monthly liquid-equivalent snowfall.
The snowy period of the year lasts for 3.7 months, from November 27 to March 17, with a sliding 31-day liquid-equivalent snowfall of at least 0.1 inches. The most snow falls during the 31 days centered around January 27, with an average total liquid-equivalent accumulation of 0.3 inches.
The snowless period of the year lasts for 8.3 months, from March 17 to November 27. The least snow falls around July 23, with an average total liquid-equivalent accumulation of 0.0 inches.
Average Liquid-Equivalent Monthly Snowfall
The length of the day in St. Louis varies significantly over the course of the year. In 2017, the shortest day is December 21, with 9 hours, 28 minutes of daylight; the longest day is June 20, with 14 hours, 52 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 5:35 AM on June 13, and the latest sunrise is 1 hour, 55 minutes later at 7:31 AM on November 4. The earliest sunset is at 4:39 PM on December 7, and the latest sunset is 3 hours, 50 minutes later at 8:29 PM on June 28.
Daylight saving time (DST) is observed in St. Louis during 2017, starting in the spring on March 12, lasting 7.8 months, and ending in the fall on November 5.
Sunrise & Sunset with Twilight and Daylight Saving Time
We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.
St. Louis experiences extreme seasonal variation in the perceived humidity.
The muggier period of the year lasts for 4.1 months, from May 20 to September 23, during which time the comfort level is muggy, oppressive, or miserable at least 18% of the time. The muggiest day of the year is July 22, with muggy conditions 71% of the time.
The least muggy day of the year is January 28, when muggy conditions are essentially unheard of.
Humidity Comfort Levels
This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.
The average hourly wind speed in St. Louis experiences mild seasonal variation over the course of the year.
The windier part of the year lasts for 7.2 months, from October 12 to May 19, with average wind speeds of more than 4.2 miles per hour. The windiest day of the year is April 1, with an average hourly wind speed of 5.3 miles per hour.
The calmer time of year lasts for 4.8 months, from May 19 to October 12. The calmest day of the year is July 31, with an average hourly wind speed of 3.0 miles per hour.
Average Wind Speed
The predominant average hourly wind direction in St. Louis varies throughout the year.
The wind is most often from the south for 10 months, from February 20 to December 22, with a peak percentage of 44% on June 21. The wind is most often from the west for 1.9 months, from December 22 to February 20, with a peak percentage of 34% on January 1.
This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.
The average daily incident shortwave solar energy experiences significant seasonal variation over the course of the year.
The brighter period of the year lasts for 4.1 months, from April 26 to August 30, with an average daily incident shortwave energy per square meter above 5.9 kWh. The brightest day of the year is July 2, with an average of 6.8 kWh.
The darker period of the year lasts for 3.1 months, from November 6 to February 9, with an average daily incident shortwave energy per square meter below 3.0 kWh. The darkest day of the year is December 23, with an average of 2.0 kWh.
Average Daily Incident Shortwave Solar Energy
For the purposes of this report, the geographical coordinates of St. Louis are 38.627 deg latitude, -90.198 deg longitude, and 446 ft elevation.
The topography within 2 miles of St. Louis contains only modest variations in elevation, with a maximum elevation change of 161 feet and an average elevation above sea level of 456 feet. Within 10 miles also contains only modest variations in elevation (308 feet). Within 50 miles contains only modest variations in elevation (892 feet).
The area within 2 miles of St. Louis is covered by artificial surfaces (88%) and water (12%), within 10 miles by artificial surfaces (66%) and cropland (22%), and within 50 miles by cropland (54%) and trees (31%).
This report illustrates the typical weather in St. Louis, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.
Temperature and Dew Point
There are 3 weather stations near enough to contribute to our estimation of the temperature and dew point in St. Louis.
For each station, the records are corrected for the elevation difference between that station and St. Louis according to the International Standard Atmosphere , and by the relative change present in the MERRA-2 satellite-era reanalysis between the two locations.
The estimated value at St. Louis is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between St. Louis and a given station.
The stations contributing to this reconstruction are: Saint Louis Downtown - Parks Airport (76%, 7 kilometers, southeast); Lambert–St. Louis International Airport (16%, 21 kilometers, northwest); and Saint Louis Regional Airport (8%, 31 kilometers, northeast).
All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Tables of the Sun, Moon and Planets , by Jean Meeus.
All other weather data, including cloud cover, precipitation, wind speed and direction, and solar flux, come from NASA's MERRA-2 Modern-Era Retrospective Analysis . This reanalysis combines a variety of wide-area measurements in a state-of-the-art global meteorological model to reconstruct the hourly history of weather throughout the world on a 50-kilometer grid.
Land Use data comes from the Global Land Cover SHARE database , published by the Food and Agriculture Organization of the United Nations.
Elevation data comes from the Shuttle Radar Topography Mission (SRTM) , published by NASA's Jet Propulsion Laboratory.
Names, locations, and time zones of places and some airports come from the GeoNames Geographical Database .
Time zones for aiports and weather stations are provided by AskGeo.com .
Maps are © Esri, with data from National Geographic, Esri, DeLorme, NAVTEQ, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, and iPC.